Giardia lamblia, a waterborne human parasite, inflicts billions of people worldwide and is a major cause of outbreaks of diarrhea in the United Sates. Chronic infection leads to malnutrition, growth retardation in children, and death. Because of its devastating consequences in impoverished countries and meager efforts expended to identify new therapies, giardiasis has been designated a World Health Organization neglected disease. The CDC classified Giardia a bioterrorism category B organism because water and food supplies could be easily compromised. Drugs used to treat giardiasis produce undesirable side effects, clinical resistance occur in both immunocompromised and immunocompetent patients, and the rate of recurrence is high. The immediate goals of this project are to identify and characterize new enzyme drug targets and to discover and develop inhibitors of these enzymes. We have carefully chosen for study several enzymes that are essential for the survival of Giardia. Each enzyme is sufficiently divergent from its human homolog to allow for selective inhibition or, better, there is no human counterpart. During the next phase of the project we will study three enzymes;fructose-1,6-biphosphate aldolase of the glycolytic pathway, carbamate kinase of the arginine dihydrolase pathway, and a class I histone deacetylase that functions in regulation of transcription. Mechanistic and structural studies will assist with the rational design and optimization of inhibitors specific to these Giardia enzymes. Assays suitable for high throughput compound library screening will be developed and the kinetic properties of hits from the screens will be analyzed to determine whether they are suitable candidates for further development. SAR and structure-assisted techniques will be employed for inhibitor optimization. Inhibitors will be evaluated for their effect on the viability of Giardia trophozoites and for their human cells cytotoxicity. The iterative process of the inhibitor development will produce lead compounds that are ready for ADME studies and animal trials. The long range goal of this project is the development of new therapeutic agents to treat giardiasis patients infected with drug-resistant Giardia lamblia strains.